The uptake of ZnO and CuO nanoparticles in the water-flea Daphnia magna under acute exposure scenarios

•A comparable Daphnia zinc uptake from the ZnO nanoparticles and Zn salt was observed.•CuO nanoparticles were ingested and adsorbed to the carapace of D. magna.•CuO nanoparticles were not internalized in the tissues or cells.•Metal ions dissolved from the ZnO and CuO nanoparticles cause the acute toxicity.

In this study the uptake of ZnO and CuO nanoparticles by Daphnia magna was tested. Daphnids were exposed during 48 h to acute concentrations of the nanoparticles and corresponding metal salts. The Daphnia zinc and copper concentration was measured and the nanoparticles were localized using electron microscopy. The aggregation and dissolution in the medium was characterized. A fast dissolution of ZnO in the medium was observed, while most CuO formed large aggregates and only a small fraction dissolved. The Daphnia zinc concentration was comparable for the nanoparticles and salts. Contrarily, a much higher Daphnia copper concentration was observed in the CuO exposure, compared to the copper salt. CuO nanoparticles adsorbed onto the carapace and occurred in the gut but did not internalize in the tissues. The combined dissolution and uptake results indicate that the toxicity of both nanoparticle types was caused by metal ions dissolved from the particles in the medium.